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Heterotic Effects in Reproduction and Growth to Weaning in Crosses of the Angus, Hereford and Shorthorn Breeds¹

University of California, Davis

Abstract

Estimates have been presented of the amount of hybrid vigor to be expected from two-way crosses of the Angus, Hereford and Shorthorn breeds for various traits. The estimator employed was the average of the reciprocal crosses minus the average of the purebreds.

The hybrid vigor estimates for gestation length, expressed as percentages of the relevant purebred means, were 0.5%, 0.5% and 0.04% for the Hereford and Angus, Hereford and Shorthorn, and Shorthorn and Angus crosses, respectively.

For birthweight, evidence was presented suggesting that more hybrid vigor is to be expected from the Hereford and Shorthorn cross than from either of the other two crosses, viz. 2.2±1.2 kg. compared to –.1±1.1 kg. and 0.2±0.9 kg. for the Hereford and Angus and Shorthorn and Angus crosses, respectively.

For weaning weight the two-way cross estimates of hybrid vigor were 7.0±4.8 kg. for the Hereford and Angus cross, 10.2±5.3 kg. for the Hereford and Shorthorn cross and 6.5±5.0 kg. for the Shorthorn and Angus cross.

There was no consistent evidence of hybrid vigor for weaning grade. Expressed as a percentage of the purebred means the average two-way cross estimate was –.1%.

For percentage calf crop weaned, (W/E), the Hereford and Shorthorn cross exhibited less hybrid vigor than the Hereford and Angus cross or the Shorthorn and Angus cross. The estimates were 8%, 15% and 14%, respectively. For the component traits of (W/E), viz., percentage of cows producing a term calf, (C/E), and percentage of term calves weaned, (W/C), the corresponding two-way cross hybrid vigor estimates were 10%, 11% and 10% for (C/E) and –3%, 4% and 3% for (W/C), respectively.

For traits expressed as percentages, the weighting and averaging of independent hybrid vigor estimates made by stations with experiments involving different numbers of breeding cows was discussed.

Breed of cow comparisons for purebred cows producing purebred and crossbred calves were made for the various traits. Possible biases in such comparisons were mentioned.

¹ Research conducted in cooperation with the Animal Husbandry Research Division, A.R.S., U.S.D.A. and as part of the W-1 Regional Beef Breeding Project.

² Present Address: Department of Veterinary Science, University of Kentucky, Lexington.